Corrosion of reinforced concrete has been usually associated with chloride ions. However, another cause of rebar corrosion is due to concrete carbonation. Carbonation-induced corrosion tends to develop later, proceeds at slower rates than chloride-induced corrosion, and leads to uniform steel corrosion that would accelerate the crack formation and decrease the structure's remaining service life. In tropical non-marine environments, carbonation-induced corrosion would be the main corrosion mechanism in reinforced concrete. The objective of this investigation was to study the effect of carbonation on concrete buildings located in urban environments. Preliminary results based on the analysis of the carbonation depth, superficial concrete strength, porosity, and water absorption show an influence of the building requirements at the time of construction. The results are compared with those obtained in a previous investigation in concrete buildings located in tropical zones. Estimates of the length of the corrosion initiation period based on the measured carbonation coefficients are presented.
The high rate of demographic growth in Mexico during the second half of the last century pushed the increment of the country's infrastructure in a large scale. One of the areas with the highest rate of growth was education, since a large amount of money has been invested in an effort to ensure a better education for the youth. During the last 30 years a large number of educational institutes have flourished around the country, and the existing ones have enlarged their facilities. The Universidad Autonoma de Yucatan (UADY), funded early in the last century, was not the exception, and during the 70's and 80's developed a plan to provide new facilities to the different campuses around the city of Merida. Most of the structures were designed and built according to specifications and construction practices commonly used at that time for up to three story buildings. The design concrete compressive strength was 20 MPa, which was the one used in Mexico before the earthquake of 1985, experience that prompted an increment in the required concrete compressive strength to 25 MPa.
On the other hand, durability of concrete structures was not a problem in the region at that time, so the design criteria for reinforced concrete were based only on the required compressive strength. Therefore, buildings were built, presumably, using concrete with a high water- cement ratio (W/C) of 0.70 or more, resulting in high porosity material. On top of the high W/C employed, it was a common practice to use concrete covers of 25 mm or less, escalating the durability problems of the concrete structures. In addition, the concrete used for these structures was prepared on site; hence a high coefficient of variation in the compressive strength is expected. Also, aggregates used were crushed limestone obtained from superficial mines with a maximum depth of seven meters.
The region climate is hot sub humid and corresponds to tropical savanna climate (Aw) in the Coppen-Geiger-Pohl classification. This environment is defined by the following characteristics: medium temperature above 18°C for the whole year, heavy rain but very dry during the months from December to March, and there is not a winter season,. Relative humidity (RH) in the region varies from 40% around noon to 99% at dawn, so the structures are subjected to permanent humidity cycles.
Based on the distance from the sea (about 40 km), it is expected that the corrosion problems were associated with concrete carbonation and not with chlorides. 1 This problem has not been studied in detail in tropical environments, hence the importance of explor
